1. Field of Invention
The present invention is directed to methods for designing contact lenses with a semi-customized back surface or base curve using a library of base curves. A base curve that best matches an individual subject's needs in terms of at least one of vision, comfort, fit, or handling, while minimizing wrapping of the contact lens on eye, is selected from the base curve library.
2. Description of Related Art
Wrapping, or flexure, occurs when a lens is placed on eye and the shape of the back surface of the lens reshapes to match the corneal geometry of the eye. For soft lenses, the back surface will substantially replicate the corneal geometry. For hard lenses, the back surface remains substantially the same. It is desirable to minimize lens wrapping so that vision correction will not be substantially affected.
Low order aberration corrections (e.g., defocus and astigmatism) are not as sensitive to lens wrapping as more complex vision corrections involving high order aberration corrections.
Minimizing the wrapping of contact lenses when correcting high order aberrations may be achieved by using corneal topography data to design a back surface or base curve of the lens. The elimination or minimization of the wrapping effect is obtained by matching the shape of the back surface of the lens within an optic zone to the corneal topography. This design approach ensures minimal change in the lens shape within the back optic zone when the contact lens is placed onto an eye.
However, manufacturing such contact lenses with a custom back surface is very expensive and time-consuming. Thus, there remains a need for semi-customization of the back surface of a contact lens to achieve a balance between design complexity, patient needs, and minimization of wrapping.